'flatline' can also refer to...

Quick Reference

Die; with reference to the continuous straight line displayed on a heart monitor, indicating death. The term is recorded in a medical context in the early 1980s, but came to general prominence with the release of the film The Flatliners (1990). The film tells the story of a group of medical students who dangerously exploit their ability to control the heart rate by helping each other to flatline in order to experience the first few seconds after the moment of death, before being revived (the participants, or flatliners, were considerably chastened by the experience).